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<body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">JSON-LD - Linked Data Expression in JSON</h1><h2 id="subtitle">A Context-based JSON Serialization for Linked Data</h2><h2 id="unofficial-draft-07-may-2011">Unofficial Draft 07 May 2011</h2><dl><dt>Editor:</dt><dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar, Inc.</a></dd>
<dt>Authors:</dt><dd><a href="http://webbackplane.com/">Mark Birbeck</a>, <a href="http://webbackplane.com/">Backplane Ltd.</a></dd>
<dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar, Inc.</a></dd>
</dl><p>This document is also available in this non-normative format: <a href="diff-20110201.html">diff to previous version</a>.</p><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
<div id="abstract" class="introductory section"><h2>Abstract</h2>
<p>
Developers that embed structured data in their Web pages can choose among
a number of languages such as RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>], Microformats [<cite><a class="bibref" rel="biblioentry" href="#bib-MICROFORMATS">MICROFORMATS</a></cite>] 
and Microdata [<cite><a class="bibref" rel="biblioentry" href="#bib-MICRODATA">MICRODATA</a></cite>]. Each of these structured data languages, while
incompatible at the syntax level, can be easily mapped to RDF. JSON has 
proven to be a highly useful object serialization and messaging format. 
In an attempt to harmonize the representation of Linked Data in JSON, 
this specification outlines a common JSON representation format for 
Linked Data that can be used to represent objects specified via RDFa, 
Microformats and Microdata.
</p>
</div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
<p>This document is an experimental work in progress.</p>

<!--  <p>
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</div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.2 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#design-goals-and-rationale" class="tocxref"><span class="secno">2. </span>Design Goals and Rationale</a><ul class="toc"><li class="tocline"><a href="#goals" class="tocxref"><span class="secno">2.1 </span>Goals</a></li><li class="tocline"><a href="#map-terms-to-iris" class="tocxref"><span class="secno">2.2 </span>Map Terms to IRIs</a></li><li class="tocline"><a href="#the-json-ld-context" class="tocxref"><span class="secno">2.3 </span>The JSON-LD Context</a></li><li class="tocline"><a href="#unambiguous-identifiers-for-json" class="tocxref"><span class="secno">2.4 </span>Unambiguous Identifiers for JSON</a></li><li class="tocline"><a href="#mashing-up-vocabularies" class="tocxref"><span class="secno">2.5 </span>Mashing Up Vocabularies</a></li><li class="tocline"><a href="#an-example-of-a-context" class="tocxref"><span class="secno">2.6 </span>An Example of a Context</a></li></ul></li><li class="tocline"><a href="#markup-examples" class="tocxref"><span class="secno">3. </span>Markup Examples</a><ul class="toc"><li class="tocline"><a href="#rdfa" class="tocxref"><span class="secno">3.1 </span>RDFa</a></li><li class="tocline"><a href="#microformats" class="tocxref"><span class="secno">3.2 </span>Microformats</a></li><li class="tocline"><a href="#microdata" class="tocxref"><span class="secno">3.3 </span>Microdata</a></li></ul></li><li class="tocline"><a href="#the-json-ld-processing-algorithm" class="tocxref"><span class="secno">4. </span>The JSON-LD Processing Algorithm</a></li><li class="tocline"><a href="#markup-of-rdf-concepts" class="tocxref"><span class="secno">5. </span>Markup of RDF Concepts</a><ul class="toc"><li class="tocline"><a href="#iris" class="tocxref"><span class="secno">5.1 </span>IRIs</a></li><li class="tocline"><a href="#identifying-the-subject" class="tocxref"><span class="secno">5.2 </span>Identifying the Subject</a></li><li class="tocline"><a href="#specifying-the-type" class="tocxref"><span class="secno">5.3 </span>Specifying the Type</a></li><li class="tocline"><a href="#plain-literals" class="tocxref"><span class="secno">5.4 </span>Plain Literals</a></li><li class="tocline"><a href="#language-specification-in-plain-literals" class="tocxref"><span class="secno">5.5 </span>Language Specification in Plain Literals</a></li><li class="tocline"><a href="#typed-literals" class="tocxref"><span class="secno">5.6 </span>Typed Literals</a></li><li class="tocline"><a href="#multiple-objects-for-a-single-property" class="tocxref"><span class="secno">5.7 </span>Multiple Objects for a Single Property</a></li><li class="tocline"><a href="#multiple-typed-literals-for-a-single-property" class="tocxref"><span class="secno">5.8 </span>Multiple Typed Literals for a Single Property</a></li><li class="tocline"><a href="#blank-nodes" class="tocxref"><span class="secno">5.9 </span>Blank Nodes</a></li></ul></li><li class="tocline"><a href="#advanced-features" class="tocxref"><span class="secno">6. </span>Advanced Features</a><ul class="toc"><li class="tocline"><a href="#automatic-typing" class="tocxref"><span class="secno">6.1 </span>Automatic Typing</a></li><li class="tocline"><a href="#type-coercion" class="tocxref"><span class="secno">6.2 </span>Type Coercion</a></li></ul></li><li class="tocline"><a href="#best-practices" class="tocxref"><span class="secno">7. </span>Best Practices</a><ul class="toc"><li class="tocline"><a href="#javascript" class="tocxref"><span class="secno">7.1 </span>JavaScript</a></li><li class="tocline"><a href="#schema-less-databases" class="tocxref"><span class="secno">7.2 </span>Schema-less Databases</a></li></ul></li><li class="tocline"><a href="#advanced-concepts" class="tocxref"><span class="secno">8. </span>Advanced Concepts</a><ul class="toc"><li class="tocline"><a href="#vocabulary-profiles" class="tocxref"><span class="secno">8.1 </span>Vocabulary Profiles</a></li><li class="tocline"><a href="#disjoint-graphs" class="tocxref"><span class="secno">8.2 </span>Disjoint Graphs</a></li><li class="tocline"><a href="#the-json-ld-api" class="tocxref"><span class="secno">8.3 </span>The JSON-LD API</a><ul class="toc"><li class="tocline"><a href="#methods" class="tocxref"><span class="secno">8.3.1 </span>Methods</a></li><li class="tocline"><a href="#methods-1" class="tocxref"><span class="secno">8.3.2 </span>Methods</a></li><li class="tocline"><a href="#methods-2" class="tocxref"><span class="secno">8.3.3 </span>Methods</a></li></ul></li></ul></li><li class="tocline"><a href="#the-default-context" class="tocxref"><span class="secno">A. </span>The Default Context</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">B. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">C. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">C.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">C.2 </span>Informative references</a></li></ul></li></ul></div>



<div id="introduction" class="section">

<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2>

JSON-LD is designed as a light-weight syntax that can be used to express 
Linked Data. It is primarily intended to be a way to express Linked Data 
in Javascript and other Web-based programming environments. It is also 
useful when building interoperable Web Services and when storing Linked 
Data in JSON-based document storage engines. It is practical and designed 
to be as simple as possible, utilizing the large number of JSON parsers 
and existing code that is in use today. It is designed to be able to 
express key-value pairs, RDF data, Microformats data, and Microdata.
That is, it supports every major Web-based structured data model in use 
today. It does not require anyone to change their JSON, but easily add 
meaning by adding context in a way that is out-of-band. The syntax is 
designed to not disturb already deployed systems running on JSON, but 
provide a smooth migration path from JSON to JSON with added
semantics. Finally, the format is intended to be fast to parse, fast to 
generate, stream-based and document-based processing compatible, and require
a very small memory footprint in order to operate.
<p></p>

<div id="how-to-read-this-document" class="section">
<h3><span class="secno">1.1 </span>How to Read this Document</h3>

<p>
This document is a detailed specification for a serialization of JSON for Linked
data. The document is primarily intended for the following audiences:
</p>

<ul>
  <li>Web developers that want to understand the design decisions and 
  language syntax for JSON-LD.</li>
  <li>Software developers that want to encode Microformats, RDFa, or Microdata 
  in a way that is cross-language compatible via JSON.</li>
  <li>Software developers that want to write processors for JSON-LD.</li>
</ul>

<p>
To understand this specification you must first be familiar with JSON, 
which is detailed in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] and [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>].</p>
</div>

<div id="contributing" class="section">
<h3><span class="secno">1.2 </span>Contributing</h3>

<p>There are a number of ways that one may participate in the development of
this specification:</p>

<ul>
<li>All comments and discussion takes place on the public mailing list:
<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
</li>

<li>Specification bugs and issues should be reported in the 
<a href="http://github.com/digitalbazaar/json-ld/issues">issue tracker</a>.</li>

<li><a href="http://github.com/digitalbazaar/json-ld">Source code</a> for the 
specification can be found on Github.</li>

<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a> 
IRC channel is available for real-time discussion on irc.freenode.net.</li>
</ul>

</div>

</div>

<div id="design-goals-and-rationale" class="section">

<!-- OddPage -->
<h2><span class="secno">2. </span>Design Goals and Rationale</h2>

<p>The following section outlines the design goals and rationale behind the 
JSON-LD markup language.
</p>

<div id="goals" class="section">
<h3><span class="secno">2.1 </span>Goals</h3>

<p>
A number of design considerations were explored during the creation of this 
markup language:
</p>

<dl>
 <dt>Simplicity</dt>
 <dd>Developers don't need to know RDF in order to use the basic functionality
 provided by JSON-LD.</dd>
 <dt>Compatibility</dt>
 <dd>The JSON-LD markup should be 100% compatible with JSON.</dd>
 <dt>Expressiveness</dt>
 <dd>All major RDF concepts must be expressible via the JSON-LD syntax.</dd>
 <dt>Terseness</dt>
 <dd>The JSON-LD syntax must be very terse and human readable.</dd>
 <dt>Zero Edits, most of the time</dt>
 <dd>JSON-LD provides a mechanism that allows developers to specify 
 context in a way that is out-of-band. This allows organizations that have
 already deployed large JSON-based infrastructure to add meaning to their
 JSON in a way that is not disruptive to their day-to-day operations and is
 transparent to their current customers. At times, mapping JSON to 
 RDF can become difficult - in these instances, rather than having JSON-LD
 support esoteric markup, we chose not to support the use case and
 support a simplified syntax instead. So, while we strive for Zero Edits,
 it was not always possible without adding great complexity to the language.
 </dd>
 <dt>Streaming</dt>
 <dd>The format supports both document-based and stream-based processing.</dd>
</dl>
</div>

<div id="map-terms-to-iris" class="section">
<h3><span class="secno">2.2 </span>Map Terms to IRIs</h3>

<p>Establishing a mechanism to map JSON values to IRIs will
help in the mapping of JSON objects to RDF. This does not mean that JSON-LD must
be restrictive in declaring a set of terms, rather, experimentation and 
innovation should be supported as part of the core design of JSON-LD. There are, 
however, a number of very small design criteria that can ensure that developers 
will generate good RDF data that will create value for the greater 
semantic web community and JSON/REST-based Web Services community.
</p>

<p>We will be using the following JSON object as the example for this section:
</p>

<pre class="example">
{
  "a": "Person",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/"
  "avatar": "http://twitter.com/account/profile_image/manusporny"
}</pre>
</div>

<div id="the-json-ld-context" class="section">
<h3><span class="secno">2.3 </span>The JSON-LD Context</h3>

<p>A context is used in RDFa to allow developers to use aliases for 
IRIs. The semantic web, just like the document-based web, uses IRIs for
unambiguous identification. The idea is that these terms mean something, 
which you will eventually want to query. The semantic web specifies this via 
<em>Vocabulary Documents</em>. The IRI <em>http://xmlns.com/foaf/0.1/</em> 
specifies a Vocabulary Document, and <strong>name</strong> is a term in 
that vocabulary. Join the two items together and you have an unambiguous 
identifier for a vocabulary term. The Compact URI Expression, or short-form,
is <code>foaf:name</code> and the expanded-form is
<code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary term identifies
the given name for something, for example - a person's name.
</p>

<p>Developers, and machines, would be able to use this IRI (plugging it
directly into a web browser, for instance) to go to the term and get a 
definition of what the term means. Much like we can use WordNet today to 
see the 
<a href="http://wordnetweb.princeton.edu/perl/webwn?s=definition">definition</a>
of words in the English language. Machines need the same sort of 
dictionary of terms, and URIs provide a way to ensure that these terms
are unambiguous.
</p>

<p>The context provides a collection of vocabulary terms that can be used
for a JSON object.</p>
</div>

<div id="unambiguous-identifiers-for-json" class="section">
<h3><span class="secno">2.4 </span>Unambiguous Identifiers for JSON</h3>
            
<p>If a set of terms, like <strong>Person</strong>, 
<strong>name</strong>, and <strong>homepage</strong>,
are defined in a context, and that context is used to resolve the
names in JSON objects, machines could automatically expand the terms to 
something meaningful and unambiguous, like this:</p>

<pre class="example">
{
  "<span class="diff">http://www.w3.org/1999/02/22-rdf-syntax-ns#type</span>": "<span class="diff">http://xmlns.com/foaf/0.1/Person</span>",
  "<span class="diff">http://xmlns.com/foaf/0.1/name</span>": "Manu Sporny",
  "<span class="diff">http://xmlns.com/foaf/0.1/homepage</span>": "http://manu.sporny.org"
  "<span class="diff">http://rdfs.org/sioc/ns#avatar</span>": "http://twitter.com/account/profile_image/manusporny"
}</pre>

<p>Doing this would mean that JSON would start to become unambiguously
machine-readable, play well with the semantic web, and basic markup wouldn't 
be that much more complex than basic JSON markup. A win, all around.</p>
</div>

<div id="mashing-up-vocabularies" class="section">
<h3><span class="secno">2.5 </span>Mashing Up Vocabularies</h3>

<p>Developers would also benefit by allowing other vocabularies to be used
automatically with their JSON API. There are over 200 
Vocabulary Documents that are available for use on the Web today. Some
of these vocabularies are:
</p>

<ul>
   <li>RDF - for describing information about objects on the semantic web.</li>
   <li>RDFS - for expressing things like labels and comments.</li>
   <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
   <li>Dublin Core - for describing creative works.</li>
   <li>FOAF - for describing social networks.</li>
   <li>Calendar - for specifying events.</li>
   <li>SIOC - for describing discussions on blogs and websites.</li>
   <li>CCrel - for describing Creative Commons and other types of licenses.</li>
   <li>GEO - for describing geographic location.</li>
   <li>VCard - for describing organizations and people.</li>
   <li>DOAP - for describing projects.</li>
</ul>

<p>Since these vocabularies are very popular, they are pre-defined in
something called the <a class="tref internalDFN" title="default_context" href="#dfn-default_context-1">default context</a>, which is a set of
vocabulary prefixes that are pre-loaded in all JSON-LD processors. The
contents of the <a class="tref internalDFN" title="default_context" href="#dfn-default_context-1">default context</a> are provided later in this 
document. Using the <a class="tref internalDFN" title="default_context" href="#dfn-default_context-1">default context</a> allows developers to 
express data unambiguously, like so:</p>

<pre class="example">
{
  "<span class="diff">rdf:type</span>": "<span class="diff">foaf:Person</span>",
  "<span class="diff">foaf:name</span>": "Manu Sporny",
  "<span class="diff">foaf:homepage</span>": "http://manu.sporny.org/",
  "<span class="diff">sioc:avatar</span>": "http://twitter.com/account/profile_image/manusporny"
}</pre>

<p>Developers can also specify their own Vocabulary documents by modifying the 
default context in-line using the <code>@context</code> keyword, like so:</p>

<pre class="example">
{
  <span class="diff">"@context": { "myvocab": "http://example.org/myvocab#" }</span>,
  "a": "foaf:Person",
  "foaf:name": "Manu Sporny",
  "foaf:homepage": "http://manu.sporny.org/",
  "sioc:avatar": "http://twitter.com/account/profile_image/manusporny"<span class="diff">,
  "myvocab:personality": "friendly"</span>
}</pre>

<p>The <code>@context</code> keyword is used to change how the JSON-LD
processor evaluates key-value pairs. In this case, it was used to
map one string ('myvocab') to another string, which is interpreted as
a IRI. In the example above, the <code>myvocab</code> string is replaced 
with "<code>http://example.org/myvocab#</code>" when it
is detected. In the example above, "<code>myvocab:personality</code>" would
expand to "<code>http://example.org/myvocab#personality</code>".</p>

<p>This mechanism is a short-hand for RDF, called a CURIE, and provides
developers an unambiguous way to map any JSON value to RDF.</p><p>

</p></div>

<div id="an-example-of-a-context" class="section">
<h3><span class="secno">2.6 </span>An Example of a Context</h3>

<p>JSON-LD strives to ensure that developers don't have to change the JSON
that is going into and being returned from their Web applications. A JSON-LD 
aware Web Service <em class="rfc2119" title="may">may</em> define a known context. For example, the
following default context could apply to all incoming Web Service calls
previously accepting only JSON data:</p>

<pre class="example">
{
  "@context": 
  {
    "@vocab": "http://example.org/default-vocab#",
    "@base": "http://example.org/baseurl/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "dc": "http://purl.org/dc/terms/",
    "foaf": "http://xmlns.com/foaf/0.1/",
    "sioc": "http://rdfs.org/sioc/ns#",
    "cc": "http://creativecommons.org/ns#",
    "geo": "http://www.w3.org/2003/01/geo/wgs84_pos#",
    "vcard": "http://www.w3.org/2006/vcard/ns#",
    "cal": "http://www.w3.org/2002/12/cal/ical#",
    "doap": "http://usefulinc.com/ns/doap#",
    "Person": "http://xmlns.com/foaf/0.1/Person",
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": "http://xmlns.com/foaf/0.1/homepage"
    "@coerce": 
    {
      "xsd:anyURI": ["foaf:homepage", "foaf:member"],
      "xsd:integer": "foaf:age"
    }
  }
}</pre>

<p>The <code>@vocab</code> string is a special keyword that states 
that any term that doesn't resolve to a term or a prefix should be 
appended to the <code>@vocab</code> IRI. This is done to ensure that 
terms can be transformed to an IRI at all times.
</p>

<p>The <code>@base</code> string is a special keyword that states 
that any relative IRI <em class="rfc2119" title="must">must</em> be appended to the string specified by
<code>@base</code>.
</p>

<p>The <code>@coerce</code> keyword is used to specify type coersion
rules for the data. For each key in the map, the key is the type to
be coerced to and the value is the vocabulary term to be coerced.
Type coersion for the key <code>xsd:anyURI</code> asserts that all 
vocabulary terms listed should undergo coercion to an IRI, including
<code>@base</code> processing for relative IRIs and CURIE processing
for compact URI Expressions like <code>foaf:homepage</code>.
</p>

</div>
</div>

<div id="markup-examples" class="section">

<!-- OddPage -->
<h2><span class="secno">3. </span>Markup Examples</h2>

<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
express semantic data marked up in other languages such as RDFa, Microformats,
and Microdata. These sections are merely provided as proof that JSON-LD is
very flexible in what it can express across different Linked Data approaches.
</p>

<div id="rdfa" class="section">
<h3><span class="secno">3.1 </span>RDFa</h3>

<p>The following example describes three people with their respective names and
homepages.</p>

<pre class="example">
&lt;div <span class="diff">prefix="foaf: http://xmlns.com/foaf/0.1/"</span>&gt;
   &lt;ul&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name" </span>&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name" </span>&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name" </span>&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;</pre>

<p>An example JSON-LD implementation is described below, however, there are
other ways to mark-up this information such that the context is not
repeated.</p>

<pre class="example">
[
 {
   "@": "_:bnode1",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/bob/",
   "foaf:name": "Bob"
 },
 {
   "@": "_:bnode2",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/eve/",
   "foaf:name": "Eve"
 },
 {
   "@": "_:bnode3",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/manu/",
   "foaf:name": "Manu"
 }
]</pre>

</div>

<div id="microformats" class="section">
<h3><span class="secno">3.2 </span>Microformats</h3>

<p>The following example uses a simple Microformats hCard example to express
how the Microformat is represented in JSON-LD.</p>

<pre class="example">
&lt;div class="vcard"&gt;
 &lt;a class="url fn" href="http://tantek.com/"&gt;Tantek Çelik&lt;/a&gt;
&lt;/div&gt;</pre>

<p>The representation of the hCard expresses the Microformat terms in the
context and uses them directly for the <code>url</code> and <code>fn</code>
properties. Also note that the Microformat to JSON-LD processor has 
generated the proper URL type for <code>http://tantek.com</code>.</p>

<pre class="example">
{
  "@context": 
  {
    "vcard": "http://microformats.org/profile/hcard#vcard",
    "url": "http://microformats.org/profile/hcard#url",
    "fn": "http://microformats.org/profile/hcard#fn",
    "@coerce": { "xsd:anyURI": "url" }
  },
  "@": "_:bnode1",
  "a": "vcard",
  "url": "http://tantek.com/",
  "fn": "Tantek Çelik"
}</pre>

</div>

<div id="microdata" class="section">
<h3><span class="secno">3.3 </span>Microdata</h3>

<p>The Microdata example below expresses book information as a Microdata Work
item.
</p>

<pre class="example">
&lt;dl itemscope
    itemtype="http://purl.org/vocab/frbr/core#Work"
    itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N"&gt;
 &lt;dt&gt;Title&lt;/dt&gt;
 &lt;dd&gt;&lt;cite itemprop="http://purl.org/dc/terms/title"&gt;Just a Geek&lt;/cite&gt;&lt;/dd&gt;
 &lt;dt&gt;By&lt;/dt&gt;
 &lt;dd&gt;&lt;span itemprop="http://purl.org/dc/terms/creator"&gt;Wil Wheaton&lt;/span&gt;&lt;/dd&gt;
 &lt;dt&gt;Format&lt;/dt&gt;
 &lt;dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596007683.BOOK"&gt;
  &lt;link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK"&gt;
  Print
 &lt;/dd&gt;
 &lt;dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596802189.EBOOK"&gt;
  &lt;link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK"&gt;
  Ebook
 &lt;/dd&gt;
&lt;/dl&gt;</pre>

<p>Note that the JSON-LD representation of the Microdata information stays
true to the desires of the Microdata community to avoid contexts and
instead refer to items by their full IRI.</p>

<pre class="example">
[
  {
    "@": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N",
    "a": "http://purl.org/vocab/frbr/core#Work",
    "http://purl.org/dc/terms/title": "Just a Geek",
    "http://purl.org/dc/terms/creator": "Whil Wheaton",
    "http://purl.org/vocab/frbr/core#realization": 
      ["http://purl.oreilly.com/products/9780596007683.BOOK", "http://purl.oreilly.com/products/9780596802189.EBOOK"]
  },
  {
    "@": "http://purl.oreilly.com/products/9780596007683.BOOK",
    "a": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK"
  },
  {
    "@": "http://purl.oreilly.com/products/9780596802189.EBOOK",
    "a": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK"
  }
]</pre>
</div>
</div>

<div id="the-json-ld-processing-algorithm" class="section">

<!-- OddPage -->
<h2><span class="secno">4. </span>The JSON-LD Processing Algorithm</h2>

<p>
The processing algorithm described in this section is provided in
order to demonstrate how one might implement a JSON-LD processor. 
Conformant implementations are only required to produce the same type and
number of triples during the output process and are not required to 
implement the algorithm exactly as described.
</p>

<p class="issue">The Processing Algorithm is a work in progress, there are
still major bugs in the algorithm and it's difficult to follow. It's provided
only to very early implementers to give them an idea of how to implement a
processor.</p>

<h4 id="processing-algorithm-terms">Processing Algorithm Terms</h4>
<ul>
<li><dfn title="default_context" id="dfn-default_context">default context</dfn> - a context that is specified to the
JSON-LD processing algorithm before processing begins.</li>
<li><dfn title="default_graph" id="dfn-default_graph">default graph</dfn> - the destination graph for all triples
generated by JSON-LD markup.</li>
<li><dfn title="active_subject" id="dfn-active_subject">active subject</dfn> - the currently active subject that the
processor should use when generating triples.</li>
<li><dfn title="inherited_subject" id="dfn-inherited_subject">inherited subject</dfn> - a subject that was detected at a
higher level of processing to be used to generate a triple once a 
<a class="tref" title="current_subject">current subject</a> is discovered or generated.</li>
<li><dfn title="active_property" id="dfn-active_property">active property</dfn> - the currently active property that the
processor should use when generating triples.</li>
<li><dfn title="inherited_property" id="dfn-inherited_property">inherited property</dfn> - a property that was detected at a
higher level of processing to be used to generate a triple once a 
<a class="tref" title="current_subject">current subject</a> is discovered or generated.</li>
<li><dfn title="active_object" id="dfn-active_object">active object</dfn> - the currently active object that the
processor should use when generating triples.</li>
<li><dfn title="active_context" id="dfn-active_context">active context</dfn> - a context that is used to resolve
CURIEs while the processing algorithm is running. The 
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> is the top-most item on the 
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> stack.</li>
<li><dfn title="local_context" id="dfn-local_context">local context</dfn> - a context that is specified at the JSON
associative-array level, specified via the <code>@context</code> keyword.</li>
<li><dfn title="list_of_incomplete_triples" id="dfn-list_of_incomplete_triples">list of incomplete triples</dfn> - A list of triples that have
yet to have their subject set.</li>
<li><dfn title="list_of_unprocessed_items" id="dfn-list_of_unprocessed_items">list of unprocessed items</dfn> - A list of objects that cannot be
processed until a <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> is detected or the end of the
current associative-array is detected.</li>
<li><dfn title="processor_state" id="dfn-processor_state">processor state</dfn> - the processor state, which includes
the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> stack, <a class="tref" title="current_subject">current subject</a>, 
<a class="tref" title="current_property">current property</a>,
<a class="tref internalDFN" title="list_of_incomplete_triples" href="#dfn-list_of_incomplete_triples">list of incomplete triples</a>, and the 
<a class="tref internalDFN" title="list_of_unprocessed_items" href="#dfn-list_of_unprocessed_items">list of unprocessed items</a>.
</li></ul>

<h4 id="processing-tokens-and-keywords">Processing Tokens and Keywords</h4>
<ul>
<li><code>@context</code> - Used to set the active context.</li>
<li><code>@base</code> - Used to set the base IRI for all object IRIs affected 
by the active context.</li>
<li><code>@vocab</code> - Used to set the base IRI for all property IRIs
affected by the active context.</li>
<li><code>@coerce</code> - Used to specify type coercion rules.</li>
<li><code>@literal</code> - Used to specify a literal value.</li>
<li><code>@iri</code> - Used to specify an IRI value.</li>
<li><code>@language</code> - Used to specify the language for a literal.</li>
<li><code>@datatype</code> - Used to specify the datatype for a literal.</li>
<li><code>:</code> - The separator for CURIEs when used in JSON keys or
JSON values.</li>
<li><code>@</code> - Sets the active subjects.</li>
<li><code>a</code> - Used to set the rdf:type of the active subjects.</li>
</ul>

<p>The algorithm below is designed for streaming (SAX-based) implementations.
Implementers will find that non-streaming (document-based) implementations will
be much easier to implement as full access to the JSON object model eliminates 
some of the steps that are necessary for streaming implementations. A conforming
JSON-LD processor <em class="rfc2119" title="must">must</em> implement a processing algorithm that results in the 
same <a class="tref internalDFN" title="default_graph" href="#dfn-default_graph">default graph</a> that the following algorithm generates:</p>

<ol class="algorithm">
<li id="processing-step-default-context">Push the <a class="tref internalDFN" title="default_context" href="#dfn-default_context-1">default context</a> 
onto the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> stack.</li>

<li id="processing-step-associative">If an associative array is 
detected, create a new
<a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>. Copy the <a class="tref" title="current_context">current context</a> stack to
the newly created <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>. Push the 
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> onto the newly created 
<a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>'s <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> stack. For each 
key-value pair in the associative array, using the newly created
<a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> do the following:

  <ol class="algorithm">

    <li>If a <code>@context</code> keyword is found, the processor
    merges each key-value pair in the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> into the
    <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>, overwriting
    any duplicate values in the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>. If the 
    <code>@coerce</code> key is found, the processor
    merges each key-value pair in the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>'s
    <code>@coerce</code> mapping into the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>'s
    <code>@coerce</code> mapping, overwriting any duplicate values in 
    the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>'s <code>@coerce</code> mapping.
    Process each object in the <a class="tref internalDFN" title="list_of_unprocessed_items" href="#dfn-list_of_unprocessed_items">list of unprocessed items</a>, 
    starting at <a href="#processing-subject">Step 2.2</a>.</li>

    <li id="processing-associative">If the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> has not 
    been detected, the current
    key-value pair is placed into the <a class="tref internalDFN" title="list_of_unprocessed_items" href="#dfn-list_of_unprocessed_items">list of unprocessed items</a>
    and processing proceeds to the next key-value pair. Otherwise, if the
    <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> is known perform the following steps:</li>

    <ol class="algorithm">

      <li id="processing-subject">If a <code>@</code> key is found, the 
      processor sets the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> to the value after 
      <a href="#markup-of-rdf-concepts">Object Processing</a> has been 
      performed.

      <ol class="algorithm">
        <li>If the <a class="tref internalDFN" title="inherited_subject" href="#dfn-inherited_subject">inherited subject</a> and 
        <a class="tref internalDFN" title="inherited_property" href="#dfn-inherited_property">inherited property</a> values are specified, generate a triple
        using the <a class="tref internalDFN" title="inherited_subject" href="#dfn-inherited_subject">inherited subject</a> for the subject, the
        <a class="tref internalDFN" title="inherited_property" href="#dfn-inherited_property">inherited property</a> for the property, and the 
        <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> for the object.
        </li>
 
        <li>If there are any triples in the 
        <a class="tref internalDFN" title="list_of_incomplete_triples" href="#dfn-list_of_incomplete_triples">list of incomplete triples</a>, complete each triple using the 
        <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> as the subject for each triple.
        </li>
      </ol>

      </li>

      <li>If an <code>a</code> key is found, set the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> 
      to <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#type</code>.
      </li>

      <li>If a key that is not <code>@context</code>, 
      <code>@</code>, or <code>a</code>, set the 
      <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> by performing 
      <a href="#markup-of-rdf-concepts">Property Processing</a> on the key.
      </li>

      <li>If the value is not an array, set the 
      <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> by performing 
      <a href="#markup-of-rdf-concepts">Object Processing</a> on the value. 
      Generate a triple representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, the
      <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>.</li>

      <li>If the value is an associative array, then
      process the value starting at 
      <a href="#processing-step-associative">Step 2</a>.</li>

      <li>If the value is a regular array, then process the value 
      starting at 
      <a href="#processing-step-array">Step 3</a> ensuring that
      the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> and the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>
      are copied to a newly created <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.</li>

      <li>If the end of the associative array is detected, and a
      <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> was not discovered, then:
      
      <ol class="algorithm">
        <li>Generate a <a class="tref" title="blank_node_identifier">blank node identifier</a> and set it as the 
        <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>.</li>

        <li>Complete any previously incomplete triples by running all substeps 
        of <a href="#processing-subject">Step 2.2.1</a>.
        </li>
      </ol>

      </li><li>If the end of the associative array is detected, and a
      <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> was not discovered, then assume that the
      <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> is unmodified and run all substeps of
      <a href="#processing-associative">Step 2.2</a>
      on the <a class="tref internalDFN" title="list_of_unprocessed_items" href="#dfn-list_of_unprocessed_items">list of unprocessed items</a>.
     </li></ol>
    </ol>
  </li>

  <li id="processing-step-array">If a regular array is detected, 
  process each value in the array by doing the following:

    <ol class="algorithm">
      <li>If the value is an associative array, processes per 
      <a href="#processing-step-associative">Step 2</a>, ensuring to set
      the <a class="tref internalDFN" title="inherited_subject" href="#dfn-inherited_subject">inherited subject</a> to the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>
      and the <a class="tref internalDFN" title="inherited_property" href="#dfn-inherited_property">inherited property</a> to the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>
      in the newly created <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.</li>

      <li>If the value is not an array, set the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> 
      by performing <a href="#markup-of-rdf-concepts">Object Processing</a> on 
      the value. Generate a triple representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, 
      the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> and 
      place it into the <a class="tref internalDFN" title="default_graph" href="#dfn-default_graph">default graph</a>.</li>

      <li>If the value is a regular array, should we support RDF 
      List/Sequence Processing? 
      <div class="issue">If the value is a regular array, should we support 
      RDF List/Sequence generation of triples? For example, would implementing
      this be worth the more complex processing rules: "ex:orderedItems" : 
      [["one", "two", "three"]]</div></li>
    </ol>
  </li>
</ol>

</div>

<div id="markup-of-rdf-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">5. </span>Markup of RDF Concepts</h2>

<p>JSON-LD is designed to ensure that most Linked Data concepts can be marked 
up in a way that is simple to understand and author by Web developers. In many
cases, Javascript objects can become Linked Data with the simple addition
of a context. Since RDF is also an important sub-community of the Linked
Data movement, it is important that all RDF concepts are well-represented
in this specification. This section details how each RDF concept can be
expressed in JSON-LD.</p>

<div id="iris" class="section">
<h3><span class="secno">5.1 </span>IRIs</h3>

<p>Expressing IRIs are fundamental to Linked Data as that is how most subjects
and many objects are identified. IRIs can be expressed in a variety of
different ways in JSON-LD.</p>

<ol>
  <li>In general, an IRI is generated if it is in the key position in 
    an associative array. There are special rules for processing keys in
    <code>@context</code> and when dealing with keys that start with the
    <code>@</code> character.</li>
  <li>An IRI is generated for the value specified using <code>@</code>, if
    it is a string.</li>
  <li>An IRI is generated for the value specified using <code>a</code>.</li>
  <li>An IRI is generated for the value specified using the <code>@iri</code> 
    keyword.</li>
  <li>An IRI is generated when there are <code>@coerce</code> rules in 
    effect for <code>xsd:anyURI</code> for a particular vocabulary term.</li>
</ol>

<p>An example of IRI generation for a key outside of a <code>@context</code>:
</p>

<pre class="example">
{
...
  "<span class="diff">http://xmlns.com/foaf/0.1/name</span>": "Manu Sporny",
...
}</pre>

<p>In the example above, the key 
<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an IRI, as 
opposed to being interpreted as a string..</p>

<p>CURIE expansion also occurs for keys in JSON-LD:</p>

<pre class="example">
{
...
  "<span class="diff">foaf:name</span>": "Manu Sporny",
...
}</pre>

<p><code>foaf:name</code> above will automatically expand out to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>.</p>

<p>An IRI is generated when a value is associated with a key using 
the <code>@iri</code> keyword:</p>

<pre class="example">
{
...
  "foaf:homepage": { "<span class="diff">@iri</span>": "http://manu.sporny.org" }
...
}</pre>

<p>If type coercion rules are specified in the <code>@context</code> for
a particular vocabulary term, an IRI is generated:</p>

<pre class="example">
{<span class="diff">
  "@context": 
  { 
    "@coerce": 
    {
      "xsd:anyURI": "foaf:homepage"
    } 
  }</span>
...
  "foaf:homepage": "http://manu.sporny.org",
...
}</pre>

</div>

<div id="identifying-the-subject" class="section">
<h3><span class="secno">5.2 </span>Identifying the Subject</h3>

<p>A subject is declared using the <code>@</code> key. The subject is the
first piece of information needed by the JSON-LD processor in order to
create the (subject, property, object) tuple, also known as a triple.</p>

<pre class="example">
{
...
  "<span class="diff">@</span>": "<span class="diff">http://example.org/people#joebob</span>",
...
}</pre>

<p>The example above would set the subject to the IRI 
<code>http://example.org/people#joebob</code>.
</p>

</div>

<div id="specifying-the-type" class="section">
<h3><span class="secno">5.3 </span>Specifying the Type</h3>

<p>The type of a particular subject can be specified using the <code>a</code>
key. Specifying the type in this way will generate a triple of the form 
(subject, type, type-url).</p>

<pre class="example">
{
...
  "@": "http://example.org/people#joebob",
  "<span class="diff">a</span>": "<span class="diff">http://xmlns.com/foaf/0.1/Person</span>",
...
}</pre>

<p>The example above would generate the following triple 
(in N-Triples notation):</p>

<pre class="example">
&lt;http://example.org/people#joebob&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

</div>

<div id="plain-literals" class="section">
<h3><span class="secno">5.4 </span>Plain Literals</h3>

<p>Regular text strings are called "plain literals" in RDF and are easily
expressed using regular JSON strings.</p>

<pre class="example">
{
...
  "foaf:name": "<span class="diff">Mark Birbeck</span>",
...
}</pre>

</div>

<div id="language-specification-in-plain-literals" class="section">
<h3><span class="secno">5.5 </span>Language Specification in Plain Literals</h3>

<p>JSON-LD makes an assumption that plain literals with associated
language encoding information is not very common when used in
JavaScript and Web Services. Thus, it takes a little more
effort to express plain literals in a specified language.</p>

<pre class="example">
{
...
  "foaf:name": <span class="diff">
  {
    "@literal": "花澄",
    "@language": "ja"
  }</span>
...
}</pre>

<p>The example above would generate a plain literal for <em>花澄</em> and
associate the <code>ja</code> language tag with the triple that is
generated. Languages <em class="rfc2119" title="must">must</em> be expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>] format.</p>

</div>

<div id="typed-literals" class="section">
<h3><span class="secno">5.6 </span>Typed Literals</h3>

<p>Literals may also be typed in JSON-LD in two ways:</p>

<ol>
  <li>By utilizing the <code>@coerce</code> keyword.</li>
  <li>By utilizing the expanded form for specifying objects.</li>
</ol>

<p>The first example uses the <code>@coerce</code> keyword to express a
typed literal:</p>

<pre class="example">
{<span class="diff">
  "@context": 
  { 
    "@coerce": 
    {
      "xsd:dateTime": "dc:modified"
    }
  }</span>
...
  "dc:modified": "2010-05-29T14:17:39+02:00",
...
}</pre>

<p>The second example uses the expanded form for specifying objects:</p>

<pre class="example">
{
...
  "dc:modified": <span class="diff">
  {
    "@literal": "2010-05-29T14:17:39+02:00",
    "@datatype": "xsd:dateTime"
  }</span>
...
}</pre>

<p>Both examples above would generate an object with the literal value of
<code>2010-05-29T14:17:39+02:00</code> and the datatype of
<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>

</div>

<div id="multiple-objects-for-a-single-property" class="section">
<h3><span class="secno">5.7 </span>Multiple Objects for a Single Property</h3>

<p>A JSON-LD author can express multiple triples in a compact way by using
arrays. If a subject has multiple values for the same property, the author
<em class="rfc2119" title="may">may</em> express each property as an array.</p>

<pre class="example">
{
...
  "@": "http://example.org/people#joebob",
  "foaf:nick": <span class="diff">["joe", "bob", "jaybee"]</span>,
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "joe" .
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "bob" .
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "jaybee" .</pre>

</div>

<div id="multiple-typed-literals-for-a-single-property" class="section">
<h3><span class="secno">5.8 </span>Multiple Typed Literals for a Single Property</h3>

<p>Multiple typed literals may also be expressed using the expanded
form for objects:</p>

<pre class="example">
{
...
  "@": "http://example.org/articles/8",
  "dcterms:modified": <span class="diff">
  [
    {
      "@literal": "2010-05-29T14:17:39+02:00",
      "@datatype": "xsd:dateTime"
    },
    {
      "@literal": "2010-05-30T09:21:28-04:00",
      "@datatype": "xsd:dateTime"
    }
  ]</span>
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">
&lt;http://example.org/articles/8&gt; 
   &lt;http://purl.org/dc/terms/modified&gt;
      "2010-05-29T14:17:39+02:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
&lt;http://example.org/articles/8&gt; 
   &lt;http://purl.org/dc/terms/modified&gt;
      "2010-05-30T09:21:28-04:00"^^http://www.w3.org/2001/XMLSchema#dateTime .</pre>

</div>

<div id="blank-nodes" class="section">
<h3><span class="secno">5.9 </span>Blank Nodes</h3>

<p>At times, it becomes necessary to be able to express information without
being able to specify the subject. Typically, this is where blank nodes come
into play. In JSON-LD, blank node identifiers are automatically created if a 
subject is not specified using the <code>@</code> keyword. However, authors 
may name blank nodes by using the special <code>_</code> CURIE prefix.</p>

<pre class="example">
{
...
  "@": "<span class="diff">_:foo</span>",
...
}</pre>

<p>The example above would set the subject to <code>_:foo</code>, which can
then be used later on in the JSON-LD markup to refer back to the 
named blank node.
</p>

</div>

</div>

<div id="advanced-features" class="section">

<!-- OddPage -->
<h2><span class="secno">6. </span>Advanced Features</h2>

<p>JSON-LD has a number of features that provide functionality above and beyond
the core functionality provided by RDF. The following sections outline the
features that are specific to JSON-LD.
</p>

<div id="automatic-typing" class="section">
<h3><span class="secno">6.1 </span>Automatic Typing</h3>

<p>Since JSON is capable of expressing typed information such as doubles, 
integers, and boolean values. As demonstrated below, JSON-LD utilizes that 
information to create <a href="#typed-literals">Typed Literals</a>:</p>

<pre class="example">
{
...
  // The following two values are automatically converted to a type of xsd:double
  // and both values are equivalent to each other.
  "measure:cups": <span class="diff">5.3</span>,
  "measure:cups": <span class="diff">5.3e0</span>,
  // The following value is automatically converted to a type of xsd:double as well
  "space:astronomicUnits": <span class="diff">6.5e73</span>,
  // The following value should never be converted to a language-native type
  "measure:stones": <span class="diff">{ "@literal": "4.8", "@datatype": "xsd:decimal" }</span>,
  // This value is automatically converted to having a type of xsd:integer
  "chem:protons": <span class="diff">12</span>,
  // This value is automatically converted to having a type of xsd:boolean
  "sensor:active": <span class="diff">true</span>,
...
}</pre>

<p class="note">When dealing with a number of modern programming languages,
including JavaScript ECMA-262, there is no distinction between 
<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is, 
the number <code>5.3</code> and the number 
<code>5.3e0</code> are treated as if they were the same. When converting from 
JSON-LD to a language-native format and back, datatype information is lost in a 
number of these languages. Thus, one could say that <code>5.3</code> is a 
<strong>xsd:decimal</strong> and <code>5.3e0</code> is an 
<strong>xsd:double</strong> in JSON-LD, but when both values are 
converted to a language-native format the datatype difference between the two 
is lost because the machine-level representation will almost always be a 
<strong>double</strong>. 
Implementers should be aware of this potential round-tripping issue between 
<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
objects with a datatype of <strong>xsd:decimal</strong> <em class="rfc2119" title="must not">must not</em> be converted
to a language native type.
</p>

</div>

<div id="type-coercion" class="section">
<h3><span class="secno">6.2 </span>Type Coercion</h3>

<p>JSON-LD supports the coercion of types to ensure that the zero-edit goal of
JSON-LD can be accomplished. Type coercion allows someone deploying JSON-LD to
coerce and incoming or outgoing types to the proper RDF type based on a
mapping of type IRIs to RDF types. Using type conversion, one may convert
simple JSON data to properly typed RDF data.</p>

<p>The example below demonstrates how a JSON-LD author can coerce values to 
plain literals, typed literals and IRIs.</p>

<pre class="example">
{
  "@context": 
  {  
     "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
     "xsd": "http://www.w3.org/2001/XMLSchema#",
     "name": "http://xmlns.com/foaf/0.1/name",
     "age": "http://xmlns.com/foaf/0.1/age",
     "homepage": "http://xmlns.com/foaf/0.1/homepage",
<span class="diff">     "@type":
     {
        "xsd:integer": "age",
        "xsd:anyURI": "homepage",
     }</span>
  },
  "name": "John Smith",
  "age": <span class="diff">"41"</span>,
  "homepage": <span class="diff">"http://example.org/home/"</span>
}</pre>

<p>The example above would generate the following triples:</p>

<pre class="example">
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/name&gt;
      "John Smith" .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      "41"^^http://www.w3.org/2001/XMLSchema#integer .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/homepage&gt;
      &lt;http://example.org/home/&gt; .</pre>

</div>

</div>

<div id="best-practices" class="section">

<!-- OddPage -->
<h2><span class="secno">7. </span>Best Practices</h2>

<p>The nature of Web programming allows one to use basic technologies, such as
JSON-LD, across a variety of systems and environments. This section attempts to
describe some of those environments and the way in which JSON-LD can be 
integrated in order to help alleviate certain development headaches.
</p>

<div id="javascript" class="section">
<h3><span class="secno">7.1 </span>JavaScript</h3>

<p class="issue">It is expected that JSON-LD will be used quite a bit in 
JavaScript environments, however, features like the expanded form for
object values mean that using JSON-LD directly in JavaScript may be 
annoying without a middleware layer such as a simple library that 
converts JSON-LD markup before JavaScript uses it. One could say that JSON-LD
is a good fit for the RDF API, which enables a variety of RDF-based
Web Applications, but some don't want to require that level of functionality 
just to use JSON-LD. The group is still discussing the best way to proceed, 
so input on how JSON-LD could more easily be utilized in JavaScript 
environments would be very much appreciated.
</p>
</div>

<div id="schema-less-databases" class="section">
<h3><span class="secno">7.2 </span>Schema-less Databases</h3>

<p class="issue">Databases such as CouchDB and MongoDB allow the creation of
schema-less data stores. RDF is a type of schema-less data model and thus
lends itself to databases such as CouchDB and MongoDB. Both of these databases
can use JSON-LD as their storage format. The group needs feedback from 
CouchDB and MongoDB experts regarding the usefulness of JSON-LD in those
environments.</p>
</div>

</div>

<div id="advanced-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">8. </span>Advanced Concepts</h2>

<p class="issue">There are a few advanced concepts where it is not clear 
whether or not the JSON-LD specification is going to support the complexity 
necessary to support each concept. The entire section on Advanced Concepts 
should be considered as discussion points; it is merely a list of 
possibilities where all of the benefits and drawbacks have not been explored.
</p>

<div id="vocabulary-profiles" class="section">
<h3><span class="secno">8.1 </span>Vocabulary Profiles</h3>

<p>One of the more powerful features of RDFa 1.1 Core is the ability to specify 
a collection of prefixes and terms that can be re-used by a processor to simplfy
markup. JSON-LD provides a similar mechanism called Vocabulary Profiles, which is 
the inclusion of a context external to the JSON-LD document.</p>

<p>The example below demonstrates how one may specify an external Vocabulary
Profile. Assume the following profile exists at this imaginary URL:
<code>http://example.org/profiles/contacts</code>.</p>

<pre class="example">
{
  "@context": 
  {
     "xsd": "http://www.w3.org/2001/XMLSchema#",
     "name": "http://xmlns.com/foaf/0.1/name",
     "age": "http://xmlns.com/foaf/0.1/age",
     "homepage": "http://xmlns.com/foaf/0.1/homepage",
     "#types":
     {
        "age": "xsd:integer",
        "homepage": "xsd:anyURI",
     }
  }
}</pre>

<p>The profile listed above can be used in the following way:</p>

<pre class="example">
{
  "@profile": "http://example.org/profiles/contacts",
  "name": "John Smith",
  "age": "41",
  "homepage": "http://example.org/home/"
}</pre>

<p>The example above would generate the following triples:</p>

<pre class="example">
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/name&gt;
      "John Smith" .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      "41"^^http://www.w3.org/2001/XMLSchema#integer .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/homepage&gt;
      &lt;http://example.org/home/&gt; .</pre>

</div>

<div id="disjoint-graphs" class="section">
<h3><span class="secno">8.2 </span>Disjoint Graphs</h3>

<p>When serializing an RDF graph that contains two or more sections of the
graph which are entirely disjoint, one must use an array to express the graph
as two graphs. This may not be acceptable to some authors, who would rather
express the information as one graph. Since, by definition, disjoint graphs
require there to be two top-level objects, JSON-LD utilizes a mechanism that
allows disjoint graphs to be expressed using a single graph.</p>

<p>Assume the following RDF graph:</p>

<pre class="example">
&lt;http://example.org/people#john&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .
&lt;http://example.org/people#jane&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

<p>Since the two subjects are entirely disjoint with one another, it is
impossible to express the RDF graph above using a single JSON-LD associative
array.</p>

<p>In JSON-LD, one can use the subject to express disjoint graphs as a 
single graph:</p>

<pre class="example">
{
  "@": 
  [
    {
      "@": "http://example.org/people#john",
      "a": "foaf:Person"
    },
    {
      "@": "http://example.org/people#jane",
      "a": "foaf:Person"
    }
  ]
}</pre>

<p>A disjoint graph could also be expressed like so:</p>

<pre class="example">
[
  {
    "@": "http://example.org/people#john",
    "a": "foaf:Person"
  },
  {
    "@": "http://example.org/people#jane",
    "a": "foaf:Person"
  }
]</pre>

</div>

<div id="the-json-ld-api" class="section">
<h3><span class="secno">8.3 </span>The JSON-LD API</h3>

<p>This API provides a clean mechanism that enables developers to convert 
JSON-LD data into a format that is easier to work with in various programming
languages.
</p>

<pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDProcessor">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">JSONLDProcessor</span> {
<span class="idlMethod">    <span class="idlMethType"><a>object</a></span> <span class="idlMethName"><a href="#widl-JSONLDProcessor-toProjection-object-DOMString-jsonld-object-template-DOMString-subject-JSONLDParserCallback-callback">toProjection</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">jsonld</span></span>, <span class="idlParam">in <span class="idlParamType"><a>object</a>?</span> <span class="idlParamName">template</span></span>, <span class="idlParam">in <span class="idlParamType"><a>DOMString</a>?</span> <span class="idlParamName">subject</span></span>, <span class="idlParam">in optional <span class="idlParamType"><a>JSONLDParserCallback</a>?</span> <span class="idlParamName">callback</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>Graph</a></span>  <span class="idlMethName"><a href="#widl-JSONLDProcessor-toGraph-Graph-DOMString-jsonld-JSONLDParserCallback-callback">toGraph</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">jsonld</span></span>, <span class="idlParam">in optional <span class="idlParamType"><a>JSONLDParserCallback</a>?</span> <span class="idlParamName">callback</span></span>);</span>
};</span>
</pre><div id="methods" class="section"><h4><span class="secno">8.3.1 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDProcessor-toGraph-Graph-DOMString-jsonld-JSONLDParserCallback-callback"><code>toGraph</code></dt><dd>Parses JSON-LD and transforms the data into an Graph, which is 
  compatible with the RDF Interfaces API specification [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-INTERFACES">RDF-INTERFACES</a></cite>]. 
  This method will 
  return <code>null</code> if there are any errors, or if the RDF Interfaces 
  API is not available for use.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">jsonld</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">The JSON-LD string to parse into the RDFGraph.</td></tr><tr><td class="prmName">callback</td><td class="prmType"><code><a>JSONLDParserCallback</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptTrue">✔</td><td class="prmDesc">A callback that is called whenever a processing error occurs on
     the given JSON-LD string.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>Graph</a></code></div></dd><dt id="widl-JSONLDProcessor-toProjection-object-DOMString-jsonld-object-template-DOMString-subject-JSONLDParserCallback-callback"><code>toProjection</code></dt><dd>Parses JSON-LD text into an RDF API Projection object as specified
    by the RDF API specification [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-API">RDF-API</a></cite>].
    If there are any errors, <code>null</code> is returned.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">jsonld</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">The JSON-LD string to parse into the Projection.</td></tr><tr><td class="prmName">template</td><td class="prmType"><code><a>object</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc">The Projection template to use when building the Projection.</td></tr><tr><td class="prmName">subject</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc">The subject to use when building the Projection.</td></tr><tr><td class="prmName">callback</td><td class="prmType"><code><a>JSONLDParserCallback</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptTrue">✔</td><td class="prmDesc">A callback that is called whenever a processing error occurs on
     the given JSON-LD string.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>object</a></code></div></dd></dl></div>

<p>The JSONLDParserCallback is called whenever a processing error occurs on
input data.</p>

<pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDProcessorCallback">[<span class="extAttr">NoInterfaceObject Callback</span>]
interface <span class="idlInterfaceID">JSONLDProcessorCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-JSONLDProcessorCallback-error-void-DOMString-error">error</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">error</span></span>);</span>
};</span>
</pre><div id="methods-1" class="section"><h4><span class="secno">8.3.2 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDProcessorCallback-error-void-DOMString-error"><code>error</code></dt><dd>This callback is invoked whenever an error occurs during processing.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">error</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">A descriptive error string returned by the processor.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>

<p>The following example demonstrates how to convert JSON-LD to a projection
that is directly usable in a programming environment:
</p>

<pre class="example">
// retrieve JSON-LD from a Web Service
var jsonldString = fetchPerson();

// This map, usually defined once per script, defines how to map incoming 
// JSON-LD to JavaScript objects
var myTemplate = { "http://xmlns.com/foaf/0.1/name" : "name",
                   "http://xmlns.com/foaf/0.1/age" : "age",
                  "http://xmlns.com/foaf/0.1/homepage" : "homepage" };

// Map the JSON-LD to a language-native object
var person = jsonld.toProjection(jsonldString, myTemplate);

// Use the language-native object
alert(person.name + " is " + person.age + " years old. " +
      "Their homepage is: " + person.homepage);</pre>

<p>A JSON-LD Serializer is also available to map a language-native object
to JSON-LD.

</p><pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDSerializer">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">JSONLDSerializer</span> {
<span class="idlMethod">    <span class="idlMethType"><a>DOMString</a></span> <span class="idlMethName"><a href="#widl-JSONLDSerializer-normalize-DOMString-object-obj">normalize</a></span> (<span class="idlParam">in <span class="idlParamType"><a>object</a></span> <span class="idlParamName">obj</span></span>);</span>
};</span>
</pre><div id="methods-2" class="section"><h4><span class="secno">8.3.3 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDSerializer-normalize-DOMString-object-obj"><code>normalize</code></dt><dd>Serializes a language-native object into a normalized JSON-LD string.
  Normalization is important when performing things like equality comparison
  and digital signature creation and verification.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">obj</td><td class="prmType"><code><a>object</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">An associative array of key-value pairs that should be converted
     to a JSON-LD string. It is assumed that a map already exists for the
     data.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>DOMString</a></code></div></dd></dl></div>

<h3 id="the-normalization-algorithm">The Normalization Algorithm</h3>

<p class="issue">This algorithm is very rough, untested, and probably contains
many bugs. Use at your own risk. It will change in the coming months.</p>

<p>The JSON-LD normalization algorithm is as follows:</p>

<ol class="algorithm">
  <li>Remove the <code>@context</code> key and preserve it as the 
  <dfn title="transformation_map" id="dfn-transformation_map">transformation map</dfn> while running this algorithm.</li>
  <li>For each key
   <ol class="algorithm">
    <li>If the key is a CURIE, expand the CURIE to an IRI using the
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
   </ol>
  </li>
  <li>For each value
   <ol class="algorithm">
    <li>If the value should be type coerced per the 
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>, ensure that it is transformed to the
        new value.</li>
    <li>If the value is a CURIE, expand the CURIE to an IRI using the
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
    <li>If the value is a Typed Literal and the type is a CURIE,
        expand it to an IRI using the <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
    <li>When generating the final value, use expanded object value form to
      store all IRIs, typed literals and plain literals with language
      information.</li>
   </ol>
  </li><li>Output each sorted key-value pair without any extraneous whitespace. If 
  the value is an associative array, perform this algorithm, starting
  at step #1, recursively on the sub-tree. There should be no nesting in
  the outputted JSON data. That is, the top-most element should be an
  array. Each item in the array contains a single subject with a 
  corresponding array of properties in UTF-8 sort order. Any related 
  objects that are complex objects themselves should be given a top-level 
  object in the top-level array.</li>
  
</ol>

<p class="issue">Note that normalizing named blank nodes is impossible at
present since one would have to specify a blank node naming algorithm. For
the time being, you cannot normalize graphs that contain named blank
nodes. However, normalizing graphs that contain non-named blank nodes 
is supported.</p>

<pre class="example">
var myObj = { "@context" : { 
                "xsd" : "http://www.w3.org/2001/XMLSchema#",
                "name" : "http://xmlns.com/foaf/0.1/name",
                "age" : "http://xmlns.com/foaf/0.1/age",
                "homepage" : "http://xmlns.com/foaf/0.1/homepage",
                "@type": {
                   "xsd:nonNegativeInteger": "age",
                   "xsd:anyURI": "homepage"
                }
              },
              "name" : "Joe Jackson",
              "age" : 42,
              "homepage" : "http://example.org/people/joe" };

// Map the language-native object to JSON-LD
var jsonldText = jsonld.normalize(myObj);</pre>

<p>After the code in the example above has executed, the 
<strong>jsonldText</strong> value will be (line-breaks added for 
readability):</p>

<pre class="example">
[{"http://xmlns.com/foaf/0.1/age":{"@datatype":"http://www.w3.org/2001/XMLSchema#nonNegativeInteger","@literal":"42"},
"http://xmlns.com/foaf/0.1/homepage":{"@iri":"http://example.org/people/joe"},
"http://xmlns.com/foaf/0.1/name":"Joe Jackson"}]</pre>

<p>When normalizing <strong>xsd:double</strong> values, implementers <em class="rfc2119" title="must">must</em>
ensure that the normalized value is a string. In order to generate the
string from a <strong>double</strong> value, output equivalent to the
<code>printf("%1.6e", value)</code> function in C <em class="rfc2119" title="must">must</em> be used where
<strong>"%1.6e"</strong> is the string formatter and <strong>value</strong>
is the value to be converted.</p>

<p>To convert the a double value in JavaScript, implementers can use the 
following snippet of code:</p>

<pre class="example">
// the variable 'value' below is the JavaScript native double value that is to be converted
(value).toExponential(6).replace(/(e(?:\+|-))([0-9])$/, '$10$2')</pre>

<p class="note">When data needs to be normalized, JSON-LD authors should
not use values that are going to undergo automatic conversion. This is due
to the lossy nature of <strong>xsd:double</strong> values.</p>

</div>

</div>



<div class="appendix section" id="the-default-context">

<!-- OddPage -->
<h2><span class="secno">A. </span>The Default Context</h2>

<p>The <dfn title="default_context" id="dfn-default_context-1">default context</dfn> is provided to ensure that there are a
reasonable set of prefixes and terms available to all JSON-LD developers.
Mappings specified by the default context <em class="rfc2119" title="should not">should not</em> be overwritten by
JSON-LD authors. All JSON-LD processors <em class="rfc2119" title="must">must</em> load the following context 
in as the intial context before processing JSON-LD text.</p>

<pre>
{
  "@context":
  {
    "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
    "rdfs": "http://www.w3.org/2000/01/rdf-schema#",
    "owl": "http://www.w3.org/2002/07/owl#",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "dcterms": "http://purl.org/dc/terms/",
    "foaf": "http://xmlns.com/foaf/0.1/",
    "cal": "http://www.w3.org/2002/12/cal/ical#",
    "vcard": "http://www.w3.org/2006/vcard/ns# ",
    "geo": "http://www.w3.org/2003/01/geo/wgs84_pos#",
    "cc": "http://creativecommons.org/ns#",
    "sioc": "http://rdfs.org/sioc/ns#",
    "doap": "http://usefulinc.com/ns/doap#",
    "com": "http://purl.org/commerce#",
    "ps": "http://purl.org/payswarm#",
    "gr": "http://purl.org/goodrelations/v1#",
    "sig": "http://purl.org/signature#",
    "ccard": "http://purl.org/commerce/creditcard#"
    "@coerce": 
    {
      "xsd:anyURI": ["foaf:homepage", "foaf:member"],
      "xsd:integer": "foaf:age"
    }
  }
}
</pre>
</div>


<div class="appendix section" id="acknowledgements">

<!-- OddPage -->
<h2><span class="secno">B. </span>Acknowledgements</h2>

<p>The editor would like to thank Mark Birbeck, who provided a great deal of the
rationale and reasoning behind the JSON-LD work via his work on RDFj, 
Dave Longley who reviewed, provided feedback, and performed several
implementation on the specification, and Ian Davis, who created RDF/JSON. 
Thanks also to Nathan Rixham, Bradley P. Allen and Richard Cyganiak for their 
input on the specification.</p>
</div>




<div id="references" class="appendix section">
<!-- OddPage -->
<h2><span class="secno">C. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">C.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-BCP47">[BCP47]</dt><dd>A. Phillips, M. Davis. <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>
</dd><dt id="bib-RDF-API">[RDF-API]</dt><dd>Manu Sporny, Benjamin Adrian, Nathan Rixham; et al. <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-api/"><cite>RDF API</cite></a> Latest. W3C Editor's Draft. URL: <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-api/">http://www.w3.org/2010/02/rdfa/sources/rdf-api/</a>
</dd><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a> 
</dd><dt id="bib-RDF-INTERFACES">[RDF-INTERFACES]</dt><dd>Nathan Rixham, Manu Sporny, Benjamin Adrian; et al. <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/"><cite>RDF Interfaces</cite></a> Latest. W3C Editor's Draft. URL: <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>
</dd><dt id="bib-RFC4627">[RFC4627]</dt><dd>D. Crockford. <a href="http://www.ietf.org/rfc/rfc4627.txt"><cite>The application/json Media Type for JavaScript Object Notation (JSON)</cite></a> July 2006. Internet RFC 4627. URL: <a href="http://www.ietf.org/rfc/rfc4627.txt">http://www.ietf.org/rfc/rfc4627.txt</a>
</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">C.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-MICRODATA">[MICRODATA]</dt><dd>Ian Hickson; et al. <a href="http://www.w3.org/TR/microdata/"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/microdata/">http://www.w3.org/TR/microdata/</a> 
</dd><dt id="bib-MICROFORMATS">[MICROFORMATS]</dt><dd><a href="http://microformats.org"><cite>Microformats</cite></a>. URL: <a href="http://microformats.org">http://microformats.org</a> 
</dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd>Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
</dd></dl></div></div></body></html>
